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Old 16th December 2004, 10:58 PM   #1
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Default Precision resistor source in Australia

I've been trying to find some 0.1% 16R2 resistors in Aus but I am having a lot of trouble.

Farnell and RS both stock Welwyn RC55Y but only down to 51R1

anyone know where I can get them from. I really don't want to have to pay $12US shipping to Mouser and have to wait 3 weeks

any brand is ok, but prefferably at least .25W, just need 4 for making a 1W 4 Ohm resistor for my walin jig II

googled on precision resistor and 0.1% resistor but have drawn a blank.

Tony.
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Old 17th December 2004, 02:00 AM   #2
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you might try searching for precision instead of a percentage
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Old 17th December 2004, 02:47 AM   #3
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Tried precision too, but nothing of use. I did some calcs and with 1% 16 ohm resistors parralled the max error will be about 0.04 ohms so I guess .1% aren't really necessary.

I'll go with the .1%'s for the 16 ohm made up of 4 X 64.9's (well close to 16.22) the actual value isn't critical, just knowing what it is is important

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Old 17th December 2004, 08:17 AM   #4
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Default Re: Precision resistor source in Australia

Quote:
Originally posted by wintermute
I've been trying to find some 0.1% 16R2 resistors in Aus but I am having a lot of trouble.
Sheesh. So where's the temperature controlled oven for them? Mercury-wetted contacts for any switches? Nay, vacuum sealed, nothing else will do!

...Not to forget you can only hear to 5%...

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Old 17th December 2004, 10:26 AM   #5
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Why not buy a number of 1% resistors and match them within 0.10 %.
Worked for me !
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Old 17th December 2004, 11:03 PM   #6
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The purpose is to use them as a reference in an impedance jig, the measurements made using the jig can only be accurate if the resistance of the reference resistors is know to a relatively high accuracy

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Old 18th December 2004, 12:01 AM   #7
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Assuming a normal distribution of values around a mean of the specified resistance, you should get excellent results by paralleling a large number of resistors of a higher value, say 100 1.62K 1% resistors. However, the accuracy you are looking for (16 milliOhms) is going to be very hard to achieve. How will you measure the resistance of your circuit board or other connections? What about your probes?

Lately I've found that ordering ,1% Dale parts from Mouser is a lot less work than ordering 1% parts and matching them. I only really required them in diff amps where the CMRR is important.
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Old 19th December 2004, 08:02 AM   #8
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yes the difficulty of measurement is exactly the reason for going with the precision parts. I only have a very ordinary DMM which hasn't got a hope of measuring low ohms accurately.

That is why I wanted the .1% resistors, then I don't have to measure them

I'm happy though with the going with 4 X 16 ohm 1% in parallel, and saying they are nominally 4 ohms... the error will only be +- .04 ohms which I don't think I'll complain about!!!

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Old 19th December 2004, 10:41 AM   #9
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I thought any ordinary DMM measures voltage within the mV range?

The resistor you need to measure is a 0.25 watt 16 Ohm resistor.
Meaning it can handle 2000 mV and 125 mA.

2000 mV can be measured by a DMM with an accuracy much better than 0.1 %.
If the lowest a DMM measures is 1 mV the accuracy for 2000 mV would be 1.0005

Build a 2 volt supply, put the voltage on a 16 Ohm resistor and measure the current with a Max741 IC.
The max741 has an accuracy of 0.1 %

1 - (1.0005/1.001) < 0.05 %
1 - (0.9995/1.001) < 0.15 %

A resistor with a 0,1 % accuracy can be anything between
0.149 % and 0.049 %


I fail to see the problem.
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Old 19th December 2004, 07:58 PM   #10
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If you have an accurate DMM to start with I know mine isn't that accurate.....

OK maybe I'm lazy, and maybe I don't want to fork out $300+ for a decent DMM, I just thought it was a lot easier/cheaper to get some accurate resistors and not have to worry about measuring them, than it was to get standard 1% types and try and measure them accurately.

The whole point with this is, that if the callibration resistors are "known" with good accuracy, then anything unknown (measured using the jig), will be measured with (hopefully) similar accuracy.

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